[vdr] Re: Coding question

["Christian Gmeiner" <christian@visual-page.de>]

Hi Klaus,

> > Christian Gmeiner wrote:
> >
> > Hi Mailingliste,
> >
> > i have here a question about coding.
> >
> > Klaus uses abstract (virtual) classes, but why is he also using the
virtual keyword in this way:
> >
> > class cDvbDevice : public cDevice {
> > private:
> >   static bool Probe(const char *FileName);
> >          ///< Probes for existing DVB devices.
> > public:
> >   static bool Initialize(void);
> >          ///< Initializes the DVB devices.
> >          ///< Must be called before accessing any DVB functions.
> >          ///< \return True if any devices are available.
> > private:
> >   fe_type_t frontendType;
> >   int fd_osd, fd_audio, fd_video, fd_dvr, fd_stc;
> > protected:
> >   virtual void MakePrimaryDevice(bool On);
> > public:
> >   cDvbDevice(int n);
> >   virtual ~cDvbDevice();
> >   virtual int ProvidesCa(const cChannel *Channel) const;
> >   virtual bool HasDecoder(void) const;
> >
> > // SPU facilities
> >
> > private:
> >   cDvbSpuDecoder *spuDecoder;
> > public:
> >   virtual cSpuDecoder *GetSpuDecoder(void);
> >
> > // Channel facilities
> >
> > private:
> >   cDvbTuner *dvbTuner;
> >   void TurnOffLiveMode(void);
> > public:
> >   virtual bool ProvidesSource(int Source) const;
> >   virtual bool ProvidesTransponder(const cChannel *Channel) const;
> >   virtual bool ProvidesChannel(const cChannel *Channel, int Priority
= -1, bool *NeedsDetachReceivers = NULL) const;
> > protected:
> >   virtual bool SetChannelDevice(const cChannel *Channel, bool LiveView);
> > public:
> >   virtual bool HasLock(void);
> >
> >
> > I always thought that i only need to use virtual on the motherclass and
the childclass dont need it.
> > In my biggest project, a game engine, i dont use virtual in the
childclass.
> > Could somebody explain this to me?
> >
> > Thanks, Christian
>
> I do it this way because I want to see immediately when looking at
> a child class which functions are virtual.
Ok thats an argument.

>
> IMHO it was a mistake of Bjarne Stroustrup to allow the 'virtual'
> keyword to be left out in child classes.
:)

Thanks Christian